1. Field of the Invention
This invention relates to an improved method of producing a blow molded product including a blow molded body portion and a tubular part embedded in the body portion by insertion, the tubular part having a hole communicating with an internal space of the body portion. This method is suited, for example, for forming an engine intake pipe. The description will hereinafter be made, taking this pipe as an example of blow molded product.
2. Prior Art
Among pipes of the type described, there is the type of pipe which is connected to another pipe at other portion than its opposite ends (that is, its peripheral wall). In this case, a tubular part such as a nipple must be embedded in the peripheral wall of the pipe.
Where the pipe has a relatively simple configuration, the pipe and the nipple can be integrally blow molded. However, when the pipe has a complicated configuration having a three-dimensionally bent portion or the like, or depending on the position of embedding of the nipple, the nipple, in some cases, can not be blow molded together with the intake pipe.
In this case, the pipe has been blow molded in the following manner.
First, a nipple is prepared, and this nipple is set, as an insert, in a blow mold. Then, a parison for forming a body portion of the pipe is inserted into the mold, and the air is blown into the parison to expand the parison into contact with the surface of the cavity. At this time, the material of the parison partially envelops the nipple, so that the nipple is embedded in the body portion of the pipe.
In the above blow molding, where the molding materials for the body portion of the pipe and the nipple are both a polyolefin-type resin such as PP, the body portion and the nipple can be fusingly bonded together, so that a relatively good airtightness between the two can be assured. The reason is considered to be that because of a relatively low melting temperature of PP or the like and of a wide temperature range of the molding, the bonding surfaces of the two are sufficiently fused at the time of the blow molding, and are connected together.
However, where the blow molding is effected using a so-called such as polyamide, the melting temperature of such material is high, and also a temperature range of the blow molding is narrow, so that airtightness can not be assured between the body portion and the nipple.